The use of processed, or granulated, cellulosic materials in animal litter is well known. For example, U.S. Pat. No. 4,374,794 to Kok illustrates a process for generating cellulosic cat litter pellets from fibrous waste sludge of the pulp and paper industries. U.S Pat. No. 4,621,011 to Fleischer et al. also describes a process for making cellulosic granules and indicates their use in cat and other animal litter.
Given the relative abundance of suitable cellulosic source material, including waste paper, cellulosic granules could be a cost-effective alternative to clay granules. In commercial practice however, the use of cellulosic granules in conventional animal litter formulations has been limited because the cellulosic granules do not provide some of the consumer-demanded features provided by clay materials. For example, conventional animal litters made up of substantial portions of cellulosic granules do not agglomerate or clump upon contact with aqueous liquids such as urine with or without conventional clumping agents.
As described in U.S. Pat. No. 5,101,771 to Goss, a clumping feature is highly desirable because it allows separation and removal of urine-soaked litter granules from an otherwise fresh bed of animal litter. Also referred to as scoopable litter because of a sieving scoop used to remove spent granules, such clumpable animal litter spares animal owners the expense and effort of full litter replacement. There continues to be a need for animal litter formulations that provide the urine clumping feature available from clay-based litters.
The use of cellulose-based granules in animal litter also has presented packaging problems because cellulosic granules readily exchange water with the surrounding atmosphere. Stated more precisely, the problem is that cellulosic granules have a relatively high water activity as compared to clay granules typically used in animal litters. Water activity is a measure of how readily product moisture is made available to the surrounding atmosphere.
To prevent spoilage during transport and storage, the humidity of air trapped above and around packaged material must be limited. Excessive package humidity stimulates microbial growth such as molding and also results in localized condensation. While bactericides can be used to limit microbial growth, the condensation problem is more troublesome because it not only damages packaging materials but also causes premature clumping of clumpable animal litters which contain cellulosic granules. Accordingly, clumpable cat litters are necessarily more sensitive to the localized condensation during storage.
One remedy for the excess humidity problem involves drying cellulosic granules to moisture levels below 3 weight percent. Such a thorough drying step adds prohibitively to the cost of producing animal litters, however.
It has now been found that an animal litter which is both packaging compatible and clumpable can be produced without excessive drying by utilizing certain combinations of adhesive-coated cellulosic granules and clay particles.